The disclosure of Japanese Patent Application No. 2001-306598 filed on Oct. 2, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a hydrogen-permeable membrane, a manufacturing method thereof, and a hydrogen gas separator using the hydrogen-permeable membrane.
2. Description of Related Art
A fuel cell system is provided with a fuel cell, a fuel gas supplying portion for supplying a fuel gas containing a hydrogen gas to the fuel cell, and an oxidizing gas supplying portion for supplying an oxidizing gas containing an oxygen gas to the fuel cell. As a method of supplying a fuel gas, there are a method of directly supplying a hydrogen gas which has been stored in a tank or a hydrogen cylinder and a method of supplying a hydrogen gas by producing the hydrogen gas from a hydrocarbon compound such as methanol. In the case where the latter method is adopted, the fuel gas supplying portion bas a reforming portion for reforming the hydrocarbon compound to the hydrogen gas.
In the reforming portion, the hydrogen gas and other gases are, in general, generated. Accordingly, in the fuel gas supplying portion, a hydrogen-permeable membrane is sometimes used in order to extract the hydrogen gas from mixed gases which have been generated in the reforming portion.
In Japanese Patent Application Laid-Open No. 11-276866, a hydrogen-permeable membrane, in which Pd (Palladium) coating layers are formed on both sides of a V (Vanadium) base layer, is disclosed. However, the hydrogen permeating membrane has a problem that hydrogen permeability deteriorates due to mutual diffusion of V and Pd.
Further, in Japanese Patent Application Laid-open No. 7-185277, a hydrogen-permeable membrane, in which an SiO2 middle layer is interposed between a V base layer and a Pd coating layer, is disclosed. Although this hydrogen-permeable membrane can reduce diffusion of V and Pd, it has a problem that hydrogen permeability of a ceramic middle layer such as SiO2 is low.
It is an object of the invention to reduce deterioration of hydrogen permeability due to mutual diffusion of metals in a hydrogen-permeable membrane.
A first aspect of the invention relates to a hydrogen-permeable membrane through which only hydrogen is selectively permeable. This hydrogen-permeable membrane is formed on a metal base layer which contains a Group VA element, a metal middle layer which is formed on at least one or first and second sides of the metal base layer and contains at least one selected element selected from Ni (Nickel) and Co (Cobalt), and a metal coating layer which is formed on a side of the metal middle layer, on which the metal base layer is not formed, and contains Pd (Palladium).
Note that the xe2x80x9cGroup VAxe2x80x9d here is also referred to as a xe2x80x9cGroup 5.xe2x80x9d
It should be noted here that a xe2x80x9csolid solubility limitxe2x80x9d means the maximum concentration (saturated concentration) of a second element which is solid-soluble to a solid made of the first element at a certain temperature. The solid solubility limit varies in accordance with a temperature and kinds of the 2 elements.
A second aspect of the invention relates to a method of manufacturing a hydrogen-permeable membrane through which only hydrogen is selectively permeable. This method includes steps of:
(a) preparing a metal base layer containing a Group VA element;
(b) forming a metal middle layer containing at least one selected element selected from Ni (Nickel) and Co (Cobalt) on at least one of first and second sides of the metal base layer, and
(c) forming a metal coating layer containing Pd (Palladium) on the side out of the two sides of the metal middle layer, on which the metal base layer is not formed.
By adopting this method, it is possible to manufacture a hydrogen-permeable membrane according to the first aspect of the invention. Also, a hydrogen gas separator having the hydrogen-permeable membrane of the first and second aspects falls within the scope of the invention.